सुखेनैव भवेद्यस्मिन्नजस्रं ब्रह्मचिन्तनम् ।आसनं तद्विजानीयान्नेतरत्सुखनाशनम् ॥ ११२ ॥
In plain words
Whatever way of sitting lets the thought of Brahman go on easily and unbroken — that is your posture. Know it as such. Not the other kind, the kind that destroys your ease.
Close to the Sanskrit
That in which the contemplation of Brahman arises easily and unceasingly — know that to be āsana; not the other, which destroys ease.